Influence of Storage Conditions on the Performance of Swab Transport Devices as Determined by the Quality Control Guidelines of NCCLS Standard M40

Most studies that have been performed to evaluate swab performance have been conducted with relatively newly produced product. The purpose of this study was to evaluate the performance of swab transport devices that had been stored for prolonged periods of time under varying conditions. We tested 6 different swab transport devices: BD CultureSwab with liquid Stuart’s (BD-LS); BD CultureSwab Plus gel with Amies (BD-GA); Starplex with liquid Stuart’s (SP-LS); Starplex gel with Amies (SP-GA); NexGen BD CultureSwab with liquid Stuart’s (NG-LS); and NexGen BD CultureSwab Plus gel with Amies (NG-GA). All of the swab transport devices utilized have rayon swabs, and none included charcoal. Swabs were stored for 9 months at 3 temperatures: refrigerated (mean temp 5.2°C, range 4.3 to 9.6°C); laboratory (mean temp.19.6°C, range 15.1 to 23.3°C); and warehouse (mean temp. 25.7°C, range 17.7 to 36.4°C). In addition, for each temperature, some swabs were maintained in the outer (foil) packaging while the remainder were stored in open (foil) packaging, providing a greater opportunity for potential desiccation and perhaps better simulating real life usage of the product.

Two of the QC organisms specified in NCCLS Standard M 40, St. pneumoniae ATCC 6305 and H. influenzae ATCC 10211, were tested utilizing the swab elution method of M- 40. Swabs were inoculated in triplicate for each variable/ swab combination that was assessed and held at 4-8°C for 48 hours prior to testing. Colony counts from swabs held for 48 hours were compared with colony counts for the same swabs at time 0. Using the M-40 standard, all swab/variable combinations for both organisms achieved acceptable results. Neither the temperature of storage nor whether the swabs were stored in open or closed outer foil packaging yielded any significant differences in results. Overall, gel based swabs had a higher percentage of recovery than swabs with liquid media. The NG-GA had the best overall recovery for the swabs tested. In conclusion, neither the temperature of storage nor the conditions of storage had any significant impact on the performance of these swab transport devices for these organisms under the conditions that were tested.